Thailand said Saturday it will ban travellers from eight southern African countries where a new Covid-19 strain has emerged.

The World Health Organization has named the new "variant of concern" Omicron, and scientists are racing to understand it and whether vaccines need adjustments.

The variant has already reached Asia and Europe with one case in Hong Kong and a confirmed infection in Belgium.

Thailand's disease control department said people from Botswana, Eswatini, Lesotho, Malawi, Mozambique, Namibia, South Africa, and Zimbabwe would be barred entry from December.

From Saturday they will be unable to register to enter the country.

"Those that have already been approved to enter the country from these eight countries will be ordered to undergo an additional 14-day mandatory quarantine, starting now," department director general Opas Karnkawinpong told reporters.

People from other African countries who have already secured approval to visit Thailand will be subject to 14 days in hotel quarantine.

Opas noted that no African countries are on a list of 63 nations eligible for quarantine-free travel to Thailand which started this month.

Thailand has recorded more than 2.1 million Covid infections, the lion's share since the Delta variant took off in April.

Only 57 percent of the population of 70 million people are fully vaccinated.